In a plant growth factory in Tsukuba, Japan, cucumber plants cultivated with spray hydroponics were wilted. The causal agent was identified as Pythium aphanidermatum based on morphological and genetic characters. Cucumber plants grafted onto squash plants as rootstocks escaped wilt in the factory, but were diseased when grafting points were infected by the pathogen. Eight major squash cultivars for rootstock for cucumber bred in Japan were not wilted after zoospores of the pathogen were mixed with the nutrient solution, however seven cucumber cultivars were wilted. Squash rootstocks would be available for suppression of Pythium root rot on hydroponic cucumbers.
